VOLCANOEVOLCANOESS

Types of Volcanoes Types of Volcanoes & Volcanic & Volcanic LandformsLandforms

TYPES OF VOLCANOESTYPES OF VOLCANOES

There are three There are three basic types of basic types of volcanoes:volcanoes:– Shield VolcanoShield Volcano– Cinder ConeCinder Cone– Composite Composite

Cone Cone (Stratovolcano)(Stratovolcano)

This diagram shows the relative sizes of the three types of volcanoes

Types of VolcanoesTypes of Volcanoes Shield VolcanoShield Volcano

– Large broad domesLarge broad domes– Mostly basaltic lavaMostly basaltic lava– Shallow slopesShallow slopes– Very little pyroclasticsVery little pyroclastics– Examples are Mona Loa Examples are Mona Loa

& Kilauea on Hawaii& Kilauea on Hawaii– Mona Loa is over 4000m Mona Loa is over 4000m

above sea level & 9000m above sea level & 9000m total from sea floor to total from sea floor to summitsummit

Top: With a Pahoehoe lava flow in the foreground, Mona Loa is shown towering in the background

Bottom: Active Kilauea crater is the summit of shield volcano

Types of VolcanoesTypes of Volcanoes Cinder ConeCinder Cone

– Small individual peaks reaching Small individual peaks reaching maximum height of 300 m maximum height of 300 m

– Made up of ejected pyroclasticsMade up of ejected pyroclastics– Steep, high angle slopesSteep, high angle slopes– Very little lava eruptedVery little lava erupted– Examples are Sunset Crater (AZ), Examples are Sunset Crater (AZ),

Mt. Capulin (NM), & Mt. Paracutin Mt. Capulin (NM), & Mt. Paracutin (Mexico)(Mexico)

– Cinder cones usually have a very Cinder cones usually have a very short life span & form in clustersshort life span & form in clusters

Top: Sunset Crater, AZ

Right: The summit of Mt. Capulin can be reached by car

Left: Diagram showing a typical cinder cone

Types of VolcanoesTypes of Volcanoes Composite Volcano (Stratovolcano)Composite Volcano (Stratovolcano)

– Large symmetrical mountainous Large symmetrical mountainous conescones

– Made of alternating lava and Made of alternating lava and pyroclastics High angle slopes ~ pyroclastics High angle slopes ~ 35°, can reach heights of 3000 m35°, can reach heights of 3000 m

– Some examples are Mt. Fuji, Mt. St. Some examples are Mt. Fuji, Mt. St. Helens, Mt. Pinatubo, Mt. Shasta, Helens, Mt. Pinatubo, Mt. Shasta, Mt. Rainer, Mt. Vesuvius, & Mt. EtnaMt. Rainer, Mt. Vesuvius, & Mt. Etna

– These are the dangerous, explosive, These are the dangerous, explosive, “Ring of Fire” volcanoes“Ring of Fire” volcanoes

Top: Pinatubo explodes in 1991

Right: Mt. Shasta is the most southern volcano in the Cascade range

Left: Mt. Rainer of the Cascades looms over nearby Seattle

Examples of Examples of U.S. Composite U.S. Composite ConesCones The entire Cascade Range in the The entire Cascade Range in the

Pacific Northwest is made up of Pacific Northwest is made up of a dozen active strato-volcanoesa dozen active strato-volcanoes

These volcanoes are explosive These volcanoes are explosive because of the type of magma because of the type of magma that erupts out of themthat erupts out of them

The subducting oceanic Juan de The subducting oceanic Juan de Fuca plate has a high amount of Fuca plate has a high amount of water dissolved in it water dissolved in it

It melts and rises up through the It melts and rises up through the continental crust and becomes continental crust and becomes more granitic (thicker, higher more granitic (thicker, higher gas content, more viscous, gas content, more viscous, etc…)etc…)

That change gives the magma That change gives the magma the potential to be very the potential to be very explosiveexplosive

Compare the three Compare the three againagain

Cinder cones are the smallest and are made of pyroclastic eruptions

Shield volcanoes are the largest and are made of lava flows

Composite volcanoes are the most dangerous and are made up of both lava flows and pyroclastic eruptions

Types of VolcanoesTypes of Volcanoes

All volcanoes can be All volcanoes can be characterized into one of characterized into one of three groups:three groups:– ActiveActive – the volcano has – the volcano has

erupted in recent times and erupted in recent times and is expected to erupt againis expected to erupt again

– DormantDormant – the volcano has – the volcano has erupted in historical times erupted in historical times and there is evidence that and there is evidence that it may erupt againit may erupt again

– ExtinctExtinct – the volcano has – the volcano has not erupted in historical not erupted in historical times and there is no times and there is no evidence that it will ever evidence that it will ever erupt againerupt again

All volcanoes have a life cycle, and some will live much longer than others depending upon the energy contained within the magma

Once the magma source beneath the cone has been completely depleted, the volcano will be come extinct

Extra-Terrestrial Extra-Terrestrial VolcanismVolcanism

Earth is not the only planet in our solar system with Earth is not the only planet in our solar system with volcanoesvolcanoes

Both Mars and Venus have large extinct volcanoesBoth Mars and Venus have large extinct volcanoes The Jovian moon IO, is the only other planetary The Jovian moon IO, is the only other planetary

body to have body to have activeactive volcanism volcanism

Left: Olympus Mons is the massive shield volcano on Mars which reaches a height of 27km; compare Mt. Everest at a height of 8.8km

Right: IO is Jupiter’s innermost moon which has dozens of active volcanoes ejecting hot gases into its atmosphere

Volcanic DestructionVolcanic Destruction

Nuee ArdenteNuee Ardente This is the other name for a This is the other name for a

pyroclastic flowpyroclastic flow A cloud of superheated gas, A cloud of superheated gas,

ash, and dust reaching ash, and dust reaching speeds of 200 km/hrspeeds of 200 km/hr

Races down mountain with Races down mountain with temps. exceeding 300°Ctemps. exceeding 300°C

Large nuee ardentes may Large nuee ardentes may travel up to 100 km or more travel up to 100 km or more and will incinerate and will incinerate everything in its patheverything in its path

Top: A nuee ardente roars down the slope of this Columbian volcano

Bottom: Click on the picture to see a nuee ardente on an island arc volcano

More Death & More Death & DestructionDestruction

LaharLahar A large mudflow that A large mudflow that

washes away and washes away and buries anything in its buries anything in its wakewake

Triggered by an Triggered by an eruption that melts the eruption that melts the ice and snow found the ice and snow found the summit of a volcanosummit of a volcano

Very dangerous and Very dangerous and quite unstoppablequite unstoppable

Top: The awesome force of lahars is evident by the burying of this car

Bottom: Click window to see video of a mini-lahar; note the muddy consistency of the water

VOLCANIC LANDFORMSVOLCANIC LANDFORMS CalderaCaldera - a large crater (1 - a large crater (1

km or more across) formed km or more across) formed when a volcano erupts, & when a volcano erupts, & collapses in on itselfcollapses in on itself

Examples are:Examples are:– Crater Lake, OR.Crater Lake, OR.– Pinatubo CalderaPinatubo Caldera– Kilauea Caldera Kilauea Caldera

Top: Diagram depicts the formation of Crater Lake

Right: Arial photo shows the 6 km wide Caldera of Crater Lake, OR

Left: The remnant of Mt. Pinatubo

More Volcanic More Volcanic LandformsLandforms

Volcanic PlugVolcanic Plug (neck)(neck)

When an extinct When an extinct volcano erodes volcano erodes and leaves behind and leaves behind the solidified the solidified magma chambermagma chamber

It is the ancient It is the ancient crystallized core of crystallized core of a volcanoa volcano Shiprock in NW New Mexico is a very

famous example of a volcanic plug

Notice the long ridge that extends from the ancient heart; this is an igneous dike

More Volcanic More Volcanic LandformsLandforms

Fissure EruptionsFissure Eruptions When very low viscosity When very low viscosity

lava pours from long lava pours from long narrow cracks in the narrow cracks in the crust it will form crust it will form extensive rivers and extensive rivers and seas of lavaseas of lava

These are made from These are made from basaltic, non-explosive basaltic, non-explosive lavas, and can flow for lavas, and can flow for 10s – 100s of km10s – 100s of km

Examples of what we Examples of what we call call flood basaltsflood basalts can be can be found in the Pacific NWfound in the Pacific NW

More Volcanic More Volcanic LandformsLandforms

Pyroclastic Flow Pyroclastic Flow DepositsDeposits – when a – when a nuee ardente nuee ardente completes its fiery completes its fiery destruction, the destruction, the fragments leave a fragments leave a very distinct very distinct depositdeposit

Top: a pyroclastic flow deposit of large block and bomb sized particles

Bottom: Note the bedding planes from the fine ash

To Review:To Review:

Volcanoes can come in Volcanoes can come in three varieties: shield three varieties: shield volcano, cinder cone, & volcano, cinder cone, & composite volcanocomposite volcano

Examples of Cinder cones:Examples of Cinder cones:– Sunset Crater, Mt. Capulin, Sunset Crater, Mt. Capulin,

and Mt. Paracutinand Mt. Paracutin Examples of Shield Examples of Shield

volcanoes:volcanoes:– Mona Loa, Kilauea, and Mona Loa, Kilauea, and

Olympus Mons (Mars)Olympus Mons (Mars) Examples of Composite Examples of Composite

volcanoes:volcanoes:– Mt. St. Helens, Mt. Rainer, Mt. St. Helens, Mt. Rainer,

Mt. Shasta, Mt. Vesuvius, Mt. Shasta, Mt. Vesuvius, Mt. Fuji, Mt. Pinatubo, and Mt. Fuji, Mt. Pinatubo, and KrakatauKrakatau

Volcanoes can be Volcanoes can be classified as either classified as either active, dormant, or active, dormant, or extinctextinct

Most death and Most death and destruction from destruction from volcanic eruptions volcanic eruptions does not come lava, does not come lava, but from pyroclastic but from pyroclastic flows and laharsflows and lahars

Volcanic landforms Volcanic landforms take on four basic take on four basic types:types:– Caldera cratersCaldera craters– Volcanic plugsVolcanic plugs– Flood basalt depositsFlood basalt deposits– Pyroclastic flow Pyroclastic flow

depositsdeposits